JPH066587A - Color correction device - Google Patents

Abstract

PURPOSE:To minimize a color difference between an original picture and a reproduced picture in all color reproduction areas by identifying whether an input color picture belongs to an area or is in existence in the vicinity of its border and implementing color correction through the use of a coefficient correcting plural sets of masking coefficients selected from the identified information. CONSTITUTION:Plural sets of prescribed masking coefficients (Mks) are stored to areas A-D of a masking coefficient (Mk) storage means 4. An area identification means 5 and a border recognition means 6 identify which area input color picture data (R1, G1, B1) belong to or are in existence in the vicinity of the border of the area and output the information. An Mk selection means 3 selects an Mk from the means 4 based on the information from the means 5, 6 and an Mk correction means 2 corrects the Mk selected by the means 3 based on the information from the means 6. Furthermore, a masking arithmetic operation means 1 uses the Mk corrected by the means 2 to apply color correction to the data R1, G1, B1 for each picture element and outputs the result. Thus, the color difference between the original picture and the reproduced picture is minimized for all color reproduction areas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction apparatus for improving color reproducibility of a color image in a color digital copying machine, a color facsimile apparatus, a color scanner, a color printer or the like.

[0002]

2. Description of the Related Art Conventionally, color correction processing called color masking has been performed in color digital copying machines, color facsimile machines, color scanners, color printers and the like. This is intended to improve the color reproducibility of color recorded images, and in color printing, it is necessary to prevent turbidity in the spectral characteristics of the printing ink and to prevent deterioration of color purity caused by non-linear distortion during color mixing. Is.

Usually, primary masking is used, but in order to correct non-linear color reproduction distortion, high-order secondary masking or 3
It is also known to use sub-masking. That is,
In the case of primary masking, the color separation signals R0, G0, B0 obtained by an actual image pickup device are subjected to the following matrix operation to obtain the corrected color separation signals R1, G1,
I have got B1. The masking coefficient used for masking can be obtained by using the least square method.

[0004]

[Equation 1]

Here, Mij is a masking coefficient. Further, as disclosed in JP-A-60-220660, the color reproduction area is divided into a plurality of areas, and a plurality of masking coefficients corresponding to the respective areas are prepared. The method of doing is also known.

[0006]

However, the conventional method has a problem that the color difference cannot be reduced even if all the color gamuts are corrected with one masking coefficient. Table 1 shows the correction results obtained by a method in which the color reproduction area is divided into a plurality of areas and a plurality of masking coefficients corresponding to the respective areas are prepared. In Table 1, No.1 to No.22, No.23 to N
o.26 and No.27 to No.30 are data in the same area, that is, they are corrected using the same masking coefficient. As can be seen from Table 1, correction distortion occurs at the area boundary.

The area dividing method used in Table 1 and each masking coefficient are described in JP-A-60-22066.
The data disclosed in Japanese Patent No. 0, No. 1 to No. 2
2 is the area A, No. 23 to No. 26 are the areas B, and No. 27 and the subsequent areas are the areas C.

[0008]

[Table 1]

Therefore, an object of the present invention is to obtain a color correction device that minimizes color differences in all color reproduction areas.

[0010]

In order to solve the above-mentioned problems, the present invention provides a color correction apparatus for inputting color image data and outputting color image data color-corrected by masking calculation means or the like, The color space of the input color image data is divided into a plurality of areas, and the masking coefficient storage means for storing the masking coefficient defined for each area, and the color space of the input color image data is divided into a plurality of areas. Then, an area identification unit that identifies to which area the input color image data belongs, and a color space of the input color image data is divided into a plurality of areas, and whether the input color image data is near the boundary of the areas. Is identified for each pixel by the boundary identifying means, the area information from the area identifying means, and the boundary neighborhood information from the boundary identifying means. Masking coefficient selection means for selecting one or more sets of masking coefficients from the storage means, and correction of one or more sets of masking coefficients selected by the masking coefficient selection means based on boundary neighborhood information from the boundary identification means. And a masking coefficient correcting means for calculating a set of masking coefficients, and a color image corrected by performing color correction for each pixel on the color image data input using the masking coefficient calculated by the masking coefficient correcting means. By having a masking calculation means for outputting data, optimum color reproduction can be achieved.

[0011]

In the color correction apparatus constructed as described above, the color space of the input color image data is divided into a plurality of areas, and the masking coefficient defined for each area is stored in the masking coefficient storage means. Keep it. When the image data is input, the area identification means identifies to which area the input color image data belongs, and the boundary identification means determines whether the input color image data is near the boundary of the area. Is identified for each pixel.

The masking coefficient selecting means selects one set or a plurality of sets of masking coefficients from the masking coefficient storing means based on the area information from the area identifying means and the boundary neighborhood information from the boundary identifying means, and masks the masking coefficients. The coefficient correcting means is selected by the masking coefficient selecting means according to the boundary neighborhood information from the boundary identifying means.
One set or a plurality of sets of masking coefficients are corrected to calculate one set of masking coefficients. Further, the masking calculation means performs color correction for each pixel on the color image data input using the masking coefficient calculated by the masking coefficient correction means, and outputs color-corrected color image data.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2A is an explanatory view conceptually showing the color space of the input color image data of the present invention, and FIG.
FIG. 4 is an explanatory diagram showing a plan view of an example of color space division of input color image data of the present invention when Green has an arbitrary value. Here, the input color image data is R1.
(Red), G1 (green), and B1 (blue), and the color-corrected output image data is R2 (red), G2 (green), and B.
2 (blue), the range of input color image data is 0 to Rmax for red, 0 to Gmax for green, and 0 to Bmax for blue.
In order to make the description easy to understand, the areas obtained by dividing the color space of the input color image data will be described as four areas (area A, area B, area C, and area D) as shown in FIG. 2B.

In FIG. 1, masking coefficient storage means 4
In the table, a plurality of sets (four sets in this embodiment) of masking coefficients defined respectively for each region (in this embodiment, region A, region B, region C, and region D) are stored in advance. Input color image data (R1, G1, B1)
Area is input, the area identification means 5 identifies to which area the input color image data (R1, G1, B1) belongs, for each pixel, and the area information (area A, area B, area C or area D). Information) to the masking coefficient selecting means 3 and the boundary identifying means 6 inputs the input color image data (R1,
It is identified for each pixel whether or not (G1, B1) is near the boundary of the region, and if it is not near the boundary, 0 is set as the boundary near information and the masking coefficient selecting means 3 and the masking coefficient correcting means 2
If it is in the vicinity of the boundary, 1 is transmitted to the masking coefficient selecting means 3 and the masking coefficient correcting means 2 as the boundary vicinity information, and further the input color image data (R1, G1, B).
1) adjacent area information (area A, area B, area C)
(Or information called area D) is used as the masking coefficient selection means 3
Tell.

Then, the masking coefficient selecting means 3 receives area information from the area identifying means 5 (information of area A, area B, area C or area D) and boundary vicinity information from the boundary identifying means 6 (0 or 0). 1) and adjacent area information (area A, area B,
One set or a plurality of sets of masking coefficients are selected from the masking coefficient storage means 4 from the area C or area D), and the masking coefficient correction means 2 selects the boundary neighborhood information (called 0 or 1) from the boundary identification means 6. The masking coefficient selecting means 3 corrects one or a plurality of masking coefficients selected by the information) to calculate one masking coefficient. Furthermore, the masking calculation means 1
Using the masking coefficient calculated by the masking coefficient correcting means 2, input color image data (R1, G1,
B1) is subjected to color correction for each pixel, and the color-corrected output color image data (R2, G2, B2) is output.

For example, input color image data (R1,
G1 and B1) belong to the area A and are not in the vicinity of the boundary of the area, the area identifying unit 5 transmits the area information of the area A to the masking coefficient selecting unit 3, and the boundary identifying unit 6 sets 0.
The boundary neighborhood information is transmitted to the masking coefficient selecting means 3 and the masking coefficient correcting means 2.

Then, the masking coefficient selecting means 3 sets a set of masking coefficients for the area A from the masking coefficient storing means 4 based on the area information of the area A from the area identifying means 5 and the boundary neighborhood information of 0 from the boundary identifying means 6. And the masking coefficient correcting means 2 does not correct the set of masking coefficients selected by the masking coefficient selecting means 3 based on the boundary neighborhood information of 0 from the boundary identifying means 6,
Further, the masking calculation means 1 performs color correction on each pixel of the input color image data (R1, G1, B1) by using the masking coefficient calculated by the masking coefficient correction means 2, and outputs the color-corrected output color image data ( R2, G
2, B2) is output.

The input color image data (R1, G
1, B1) belongs to the area A and is near the boundary of the area of the area B, the area identifying means 5 transmits the area information of the area A to the masking coefficient selecting means 3 and the boundary identifying means 6
Is the boundary neighborhood information of 1 and the masking coefficient selection means 3
To the masking coefficient correction means 2, and further to the masking coefficient selection means 3 the adjacent area information of area B.

Then, the masking coefficient selecting means 3 receives the area information of the area A from the area identifying means 5, the boundary neighborhood information of 1 from the boundary identifying means 6 and the boundary identifying means 6.
The masking coefficient correction means 2 selects two sets of masking coefficients for the areas A and B from the adjacent area information of the area B from the masking coefficient storage means 4, and the masking coefficient correction means 2 performs masking with the boundary neighborhood information of 1 from the boundary identification means 6. The two masking coefficients selected by the coefficient selecting means 3 are corrected to calculate one masking coefficient.

Further, the masking calculation means 1 uses the masking coefficient calculated by the masking coefficient correction means 2 to perform color correction on each pixel of the input color image data (R1, G1, B1) and output color corrected color. The image data (R2, G2, B2) is output.

[0021]

As described above, according to the present invention, the masking coefficient storing means 4, the area identifying means 5 for identifying the area to which the input color image data belongs, and whether the input color image data is near the boundary of the areas. A boundary identifying means 6 for identifying the masking coefficient, a masking coefficient selecting means 3 for selecting one or a plurality of masking coefficients based on the area information and the boundary vicinity information, and a masking coefficient correction for correcting the masking coefficient selected by the boundary vicinity information. Means 2 and masking calculation means 1 for performing color correction using the corrected masking coefficient
With this configuration, there is an effect that the color difference between the original image and the reproduced image can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a color correction apparatus of the present invention.

FIG. 2A is an explanatory view conceptually showing a color space of input color image data of the present invention. (B) is an explanatory view showing an example of division of a color space of input color image data of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Masking calculation means 2 Masking coefficient correction means 3 Masking coefficient selection means 4 Masking coefficient storage means 5 Area identification means 6 Boundary identification means

Claims (1)

[Claims] 1. A color correction device for inputting color image data and outputting color image data color-corrected by masking calculation means or the like, wherein a color space of the input color image data is divided into a plurality of areas, and each area is divided into a plurality of areas. On the other hand, masking coefficient storage means for storing masking coefficients respectively determined, area identifying means for identifying to which area of the color space the input color image data belongs, and the input color image data The masking coefficient is determined by a boundary identifying means for identifying for each pixel whether or not the area is near the boundary of the area identified by the area identifying means, and the area information from the area identifying means and the boundary vicinity information from the boundary identifying means. Masking coefficient selecting means for selecting one or a plurality of masking coefficients from the storing means, and boundary neighborhood information from the boundary identifying means. A masking coefficient correcting means for correcting one set or a plurality of sets of masking coefficients selected by the masking coefficient selecting means to calculate one set of masking coefficients, and a masking coefficient calculated by the masking coefficient correcting means. A color correction device comprising: masking calculation means for performing color correction on the input color image data for each pixel and outputting the color-corrected color image data.